We have recently isolated a blue light photoreceptor protein from Arabidopsis thaliana (plants); this is the first such photoreceptor to be identified in any organism. The photoreceptor appears structurally similar to microbial photolyases (DNA repair enzymes). Photolyases bind two chromophores; one of which (methenyl tetrahydrofolate) serves as a light-harvesting antenna for the other (catalytic) flavin chromophore. It has recently been determined that the blue light photoreceptor similarly binds two chromophores. It is accordingly the goal of our study to utilize the facilities of the RLBL to determine whether energy transfer of the type observed in photoreceptor for such studies. Once the parameters for energy transfer are established in the wild-type photoreceptor protein, we will supply mutant photoreceptor proteins which have been determined to be biologically inactive. Data on both wild-type and mutant proteins should supply valuable insight into the mec hanism of action of our novel photoreceptor and may illuminate features of inter-chromophore energy transfer that will have general relevance. We are presently studying the photostability of these systems.